JPH04325710A - Exhaust device of engine - Google Patents

Abstract

PURPOSE:To enhance purification performance of a catalyst by eliminating the influence by flow-out intake air on the catalyst in an engine in which flow- out of intake air into the exhaust system is large. CONSTITUTION:In the combustion chamber of an engine there are provided a first exhaust port 5 and a second exhaust port 6, and the timing of opening the first exhaust port 5 is set to be earlier, in comparison with that of the second exhaust port 6. A catalyst device 19 consisting of a ternary catalyst is provided in a first exhaust path 16 connected to the first exhaust port 5 and an exhaust sensor 20 is provided upstream thereof. Respective exhaust paths 16, 17 are connected to a collective path 18 on the downstream side. The valve opening area(lift quantity, valve diameter, valve opening period) of an exhaust valve on the side of the first exhaust port 5 may be set to be smaller, in comparison with that on the side of the second exhaust port 6.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust system for an engine, such as a two-stroke engine, in which a large amount of intake air blows through to the exhaust system.

0002

2. Description of the Related Art Generally, an engine exhaust system is provided with a catalyst device for purifying NO, CO, and HC contained in exhaust gas. The catalysts used in this catalyst device are divided into three types depending on the reaction: oxidation catalyst, reduction catalyst, and three-way catalyst.The oxidation catalyst promotes the oxidation reaction of CO and HC, and the reduction catalyst promotes the reduction reaction of NO. . Further, a three-way catalyst simultaneously performs an oxidation reaction of CO and HC and a reduction reaction of NO at a certain oxygen concentration (stoichiometric air-fuel ratio). Further, the above-mentioned catalyst device is usually used, for example, in Japanese Patent Application Laid-Open No.
As described in Japanese Patent No. 201313, the exhaust manifold is disposed downstream of the collection part of the exhaust manifold.

0003

[Problems to be Solved by the Invention] By the way, in engines where a large amount of intake air blows through to the exhaust system, such as a 2-stroke engine or a 4-stroke engine with large valve overlap, the intake air blows through without participating in combustion. Since a large amount of oxygen flows into the exhaust system, the exhaust system temporarily becomes in an oxygen-rich state. Therefore, when a catalytic device consisting of a three-way catalyst or a reduction catalyst is installed in the exhaust system of such an engine, the catalyst in the catalytic device adsorbs a large amount of oxygen and is unable to release it. There is a problem that the rate decreases.

The present invention has been made in view of the above-mentioned problems, and is intended to improve the purification performance of the catalyst by eliminating the influence of the intake air flowing through the catalyst in an engine in which a large amount of intake air blows through to the exhaust system. The purpose of this invention is to obtain an exhaust system for an engine that can

[0005]

[Means for Solving the Problems] An engine exhaust system according to the present invention is an engine exhaust system that has a blow-through period in which intake air blows through by communicating an intake port and an exhaust port, and has a blow-through period in which intake air blows through by communicating with an intake port and an exhaust port. A first catalytic device consisting of a three-way catalyst or a reduction catalyst and a second catalytic device consisting of an oxidation catalyst are arranged in series, and the exhaust gas mixed with blow-through intake air is bypassed through the first catalytic device and connected to the second catalytic converter. It is characterized by providing a bypass passage leading to the device.

The present invention also provides an exhaust system for an engine having a blow-through period in which intake air blows through due to communication between an intake port and an exhaust port, which includes an injector that directly injects fuel into the combustion chamber of each cylinder of the engine. , each cylinder is provided with a plurality of exhaust ports that open and close at different timings, and a catalyst device is disposed downstream of the exhaust port that opens at the earliest timing.

[0007] Here, the above-mentioned catalyst device can be a three-way catalyst or a catalyst device comprising a reduction catalyst.

[0008] In that case, the plurality of exhaust ports can be arranged so as to gather at a downstream collecting part, and a catalyst device comprising an oxidation catalyst can be provided downstream of this collecting part.

Furthermore, the exhaust port that opens at the earliest timing can be configured to have the smallest opening area.

Furthermore, when the catalyst device is a three-way catalyst, an exhaust sensor is provided downstream of the exhaust port that opens at the earliest timing, and the injector injects air based on the output of the exhaust sensor. It is preferable to provide a fuel control means for correcting the fuel supply amount and feedback-controlling the air-fuel ratio.

[0011]

[Operation] Blow-through intake air containing a large amount of oxygen bypasses the first catalyst device and is guided to the second catalyst device on the downstream side. Therefore, the three-way catalyst or reduction catalyst in the first catalyst device is used in the most activated state without being affected by the blow-by intake air, and the blow-by intake air has a better purification rate in an oxygen-excess state than the oxidation catalyst. The purification performance of the catalyst is improved as a whole.

In addition, as a more specific configuration, a plurality of exhaust ports with different opening and closing timings are provided for each cylinder of the engine, and a catalyst device consisting of a three-way catalyst or a reduction catalyst is installed downstream of the exhaust port that opens at the earliest timing. With this arrangement, exhaust gas at the beginning of the exhaust stroke is guided to this catalyst device, so the influence of blow-by intake air on the catalyst of the catalyst device is eliminated, and the reaction of the catalyst is improved.

In this case, if the plurality of exhaust ports are assembled on the downstream side and a catalyst device comprising an oxidation catalyst is provided downstream of the collection point, CO and HC in the exhaust gas are further removed by the oxidation catalyst. Purification performance improves.

Furthermore, if the opening area of the exhaust port that opens at the earliest timing is minimized, the blow-through intake air in the latter half of the exhaust stroke will be difficult to flow through the catalyst device consisting of a three-way catalyst or a reduction catalyst, and the purification of these catalysts will be reduced. rate is improved.

[0015] Furthermore, by providing an exhaust sensor downstream of the exhaust port that opens at the earliest timing, and controlling the amount of fuel injected from the injector based on the output of this exhaust sensor, the three-way catalyst can be The air-fuel ratio can be accurately controlled during use.

[0016]

[Embodiment] Hereinafter, an embodiment will be explained based on the drawings.

FIG. 1 is an overall system diagram of an embodiment of the present invention, and FIG. 2 is a schematic diagram of an exhaust system of an engine according to the embodiment. In this embodiment, the engine 1 is a uniflow two-stroke engine with in-cylinder direct injection, and the cylinder 2
and a piston 3 that reciprocates within the cylinder 2. A scavenging port 4 is formed in the lower part of the cylinder 2, and two exhaust ports consisting of a first exhaust port 5 and a second exhaust port 6 are formed in the head portion of the cylinder 2. Further, the head section is provided with a first exhaust valve 7 and a second exhaust valve 8, which are driven by a valve mechanism (not shown) in synchronization with the rotation of the crankshaft to open and close each of the exhaust ports 5, 6, respectively. Further, a spark plug 9 and an injector 10 for fuel injection are arranged.

An intake passage 12 extending from an air cleaner 11 is communicated with the scavenging port 4, and an air flow meter 13 for detecting the amount of intake air is provided in the intake passage 12 immediately downstream of the air cleaner 11. A mechanical supercharger 15 is also provided downstream of the throttle valve 14 .

Each exhaust port 5, 6 has a first exhaust passage 1.
6 and a second exhaust passage 17 are connected to each other, and these exhaust passages 16 and 17 are combined into one collective passage 18 on the downstream side. And the first exhaust passage 1
6 is provided with a catalyst device 19 consisting of a three-way catalyst, and
An exhaust sensor (O2 sensor) 2 is provided upstream of this catalyst device 19.
0 is placed.

Each of the exhaust valves 7 and 8 has the same opening period and lift amount, and the first exhaust valve 7 opens and closes earlier, and the second exhaust valve 8 opens and closes faster than the first exhaust valve. 7 begins to open at a predetermined crank angle after opening,
It is set to close at a predetermined crank angle after the first exhaust valve 7 closes. In addition, the scavenging port 4 is the second
The first exhaust valve 8 starts opening at a predetermined crank angle after the second exhaust valve 8 is opened, and is opened and closed by the piston 3 so as to close at a predetermined crank angle after the second exhaust valve 8 is closed.

Further, a control unit 21 consisting of a microcomputer is provided, and the control unit 21 receives an intake air amount signal from the air flow meter 13, an air-fuel ratio signal from the exhaust sensor 20, an engine rotation speed signal, etc. Various signals are input as information. The control unit 21 calculates the fuel injection amount and the like based on this information, and outputs the control signal to the injector 10 and the like. This fuel injection amount is determined by multiplying the value calculated based on the intake air amount (Q) and engine speed (N) by the blow-through correction map value (CA) as the basic amount (TP). It is determined by multiplying the output of the sensor 20 by a feedback correction value (CFB), and an injection signal having a pulse width corresponding to the thus calculated fuel injection amount is output to the injector 10.

FIG. 3 is a flowchart for executing fuel injection control in this embodiment. Note that S1 to S13 indicate each step.

In this flowchart, when started, various signals such as intake air amount Q and engine speed N are read in S1, and then, in S2, intake air amount Q is read.
The basic injection amount TP is calculated by dividing the value by the engine rotational speed N by a constant K, and further by the map value CA for blow-through correction.

Next, in S3, it is determined whether the lean side control flag F is set (F=1), and if it is set,
In S4, it is determined whether the output of the O2 sensor is on the rich side. Note that as the O2 sensor, a type of sensor whose output changes after the excess air ratio λ=1 is used. If this determination is YES, that is, if it is determined that it is on the rich side, the process goes to S5 and the feedback correction value CFB is
is lowered by the I value, the basic injection amount TP is multiplied by CFB in S6 to find the pulse width corresponding to the final injection amount, and injection is executed in S7.

[0025] After repeating S5 several times and gradually lowering the CFB, if the sensor output changes to the lean side in S4, go to S8 and raise the CFB by the P value.
9 clears flag F. Then, the process goes to S6 to calculate the injection pulse width T at this time, and executes the injection in S7.

Then, returning to S3, this time the flag F
is not 1, so go to S10 and check whether the sensor output is still on the lean side. If it is on the lean side, go to S1
1, the CFB is raised by the I value and the process proceeds to S6.

[0027] Also, by repeating S11 several times, C
While raising the FB, if the sensor output changes to the rich side in S10, the CFB is lowered by the P value in S12, the flag F is set in S13, and the process proceeds to S6.

In this embodiment, the air-fuel ratio feedback control as described above is performed based on the output of the exhaust sensor 20 provided on the side of the first exhaust port 5, which opens at an early timing. Therefore, the output of the exhaust sensor 20 is not affected by the blow-by intake air, thereby making it possible to accurately control the air-fuel ratio. Further, in this way, the exhaust gas at the beginning of the exhaust stroke is guided to the catalyst device 19 from the first exhaust port 5 and the first exhaust passage 16, and
Since the blow-by intake air generated in the latter half of the exhaust stroke is guided from the second exhaust port 6 to the second exhaust passage 17, the blow-by intake air does not flow into the catalyst device 19, and the blow-by intake air does not reach the catalyst of the catalyst device 19. influence is eliminated,
This improves the reaction of the catalyst.

FIG. 4 shows a modification of the above embodiment. In this example, the exhaust valve diameter (opening area) of the first exhaust port 5', which opens at an early timing, is made smaller than the exhaust valve diameter (opening area) of the second exhaust port 6'. In this way, the exhaust gas mixed with a large amount of blow-by air becomes difficult to flow to the catalyst device 19 provided on the first exhaust passage 16' side, and the influence of blow-by air is more reliably eliminated.

FIG. 5 shows another modification of the above embodiment. In this example, the lift amount a of the exhaust valve on the first exhaust port side is set smaller than the lift amount b of the exhaust valve on the second exhaust port side. The opening area is made smaller.

FIG. 6 shows still another modification of the above embodiment. In this example, by setting the opening period c of the exhaust valve on the first exhaust port side to be smaller than the opening period d of the exhaust valve on the second exhaust port side,
Aiming for the same effect as above.

In each of the modifications shown in FIGS. 4 to 6 above, the first exhaust port side and the second exhaust port side are different in valve diameter, lift amount, or valve opening period. However, it is also possible to combine two or three of these valve diameter, lift amount, and valve opening period.

Further, in the above embodiment, a catalyst device made of a three-way catalyst is arranged in the first exhaust passage, but instead of this, a catalyst device made of a reduction catalyst is arranged. Good too. When the reduction catalyst is disposed in this way, a catalyst device made of an oxidation catalyst may be disposed in the exhaust passage downstream of the meeting point of the first exhaust passage and the second exhaust passage. , CO, and HC purification performance can be further improved.

[0034]

[Effects of the Invention] Since the present invention is configured as described above, in an engine in which a large amount of intake air blows through to the exhaust system, the influence of the blow-by air on the catalyst is eliminated, and the purification performance of the catalyst is improved. It is also possible to accurately control the air-fuel ratio.

[Brief explanation of drawings]

[Figure 1] Overall system diagram of an embodiment of the present invention

[Fig. 2] A schematic configuration diagram of the exhaust system of the engine according to the same embodiment.

[Fig. 3] Flowchart for executing fuel injection control in the same embodiment.

[Fig. 4] A schematic configuration diagram of an exhaust system showing a modification of the same embodiment.

[
Figure 5: Exhaust valve lift characteristic diagram showing other modified examples

[
Figure 6: Exhaust valve lift characteristic diagram showing another modified example

[Explanation of symbols]

1 Engine 4 Scavenging port 5, 5' First exhaust port 6, 6' Second exhaust port 10 Injector 13 Air flow meter 16, 16' First exhaust passage 17, 17' Second exhaust passage 18 Gathering passage 19 Catalyst device 20 Exhaust sensor 21 Control unit

Claims (6)

[Claims] 1. An exhaust system for an engine having a blow-through period in which intake air blows through due to communication between an intake port and an exhaust port, the first catalyst device comprising a three-way catalyst or a reduction catalyst downstream of the exhaust port. and a second catalyst device comprising an oxidation catalyst are arranged in series, and a bypass passage is provided for guiding exhaust gas mixed with blow-through intake air to the second catalyst device by bypassing the first catalyst device. Exhaust system for the engine. 2. An exhaust system for an engine having a blow-through period in which intake air blows through due to communication between an intake port and an exhaust port, comprising: an injector that directly injects fuel into the combustion chamber of each cylinder of the engine; What is claimed is: 1. An exhaust system for an engine, comprising: a plurality of exhaust ports having different opening/closing timings; and a catalyst device disposed downstream of the exhaust port that opens at the earliest timing. 3. The engine exhaust system according to claim 2, wherein the catalyst device is a three-way catalyst or a reduction catalyst. 4. The exhaust system for an engine according to claim 3, wherein the plurality of exhaust ports are configured to gather at a downstream gathering portion, and a catalyst device comprising an oxidation catalyst is provided downstream of the gathering portion. 5. The engine exhaust system according to claim 2, wherein the opening area of the exhaust port that opens at the earliest timing is minimized. 6. The catalyst device is a three-way catalyst, and an exhaust sensor is provided upstream of the catalyst device on the downstream side of the exhaust port that opens at the earliest timing. 6. The exhaust system for an engine according to claim 5, further comprising fuel control means for correcting the amount of fuel supplied from the injector and feedback-controlling the air-fuel ratio.